Disc drives are digital data storage devices which enable users of computer systems to store and retrieve large amounts of data in a fast and efficient manner. Disc drives of the present generation have data storage capacities in excess of several gigabytes (GB) and can transfer data at sustained rates of several megabytes (MB) per second.
A typical disc drive is provided with a plurality of magnetic recording discs which are mounted to a rotatable hub of a spindle motor for rotation at a constant, high speed. An array of read/write heads are disposed adjacent surfaces of the discs to transfer data between the discs and a host computer. The heads are radially positioned over the discs by a closed loop, digital servo system, and are caused to fly proximate the surfaces of the discs upon air bearings established by air flow set up by the high speed rotation of the discs.
A plurality of nominally concentric tracks are defined on each disc surface, with disc drives of the present generation having track densities in excess of 7,000 tracks per centimeter (18,000 tracks per inch). A preamp and driver circuit generates write currents that are used by the head to selectively magnetize the tracks during a data write operation and amplifies read signals detected by the head during a data read operation. A read/write channel and interface circuit are operably connected to the preamp and driver circuit to transfer the data between the discs and the host computer.
A rigid housing is provided to support the spindle motor and the actuator and to form an internal controlled environment to minimize particulate contamination of the discs and heads. A printed wiring assembly (PWA) is mounted to the exterior of the housing to accommodate the disc drive control electronics (including the aforementioned servo circuit, read/write channel and interface circuit).
Disc drives are often used in a stand-alone fashion, such as in a typical personal computer (PC) configuration where a single disc drive is utilized as the primary data storage peripheral device. However, in applications requiring vast amounts of data storage capacity or high input/output (I/O) bandwidth, a plurality of drives can be arranged into a multi-drive array, sometimes referred to as a RAID ("Redundant Array of Inexpensive Discs"; also "Redundant Array of Independent Discs"). A seminal article proposing various RAID architectures was published in 1987 by Patterson et al., entitled "A Case for Redundant Arrays of Inexpensive Discs (RAID)", Report No. UCB/CSD 87/391, December 1987, Computer Science Division (EECS), University of California, Berkeley, Calif.
Since their introduction, RAIDs have found widespread use in a variety of applications requiring significant data transfer and storage capacities. It is presently common to incorporate several tens, if not hundreds, of drives into a single RAID. While advantageously facilitating generation of large scale data storage systems, however, the coupling of multiple drives within the same enclosure can also set up undesirable vibrations from excitation sources within the drives, such as spindle motors used to rotate the discs and actuators used to move the heads to various tracks on the discs. Such vibrations can be transmitted from drive to drive through chassis mounts used to secure the drives within the enclosure.
Vibrational components can be characterized as translational, or rotational. Translational vibrations tend to move a disc drive housing back and forth along a plane of the drive, whereas rotational vibrations tend to rotate a disc drive housing about an axis normal to a plane of the drive. Translational vibrations will generally have a smaller effect upon the ability of the actuator to maintain the heads at a selected position with respect to the discs, as the discs and the actuator will both respond to the movement induced by such translational vibrations. Particularly, disc drive designers typically attempt to provide balanced actuators to minimize actuator rotation during a translational vibration event.
However, such is not true with rotational vibrations. Even with a nominally balanced actuator, rotational vibrations will tend to move the discs relative to the actuator because the actuator, acting as a free body, remains essentially undisturbed due to inertial effects while the discs, mounted to the housing, are displaced by imparted rotational vibration. When sufficiently severe, such movement will cause an "off-track" condition whereby a head is moved away from a selected track being followed. Such off-track conditions can adversely affect the ability of the drive to transfer data between the discs and host device.
Known methods of reduction of the negative effects associated with disc drive mechanical resonances have generally followed the pattern of attempting to make all components sufficiently stiff so that their resonant frequencies are made as high as possible. Although this appears to be a sensible procedure, it often suffers from the problem that, although the resonance frequency is increased, the mechanical "gain" or "Q" at resonance also increases, thus tending to reduce the bandwidth improvement that might otherwise be expected. Reducing the gain by, for example, change in geometry or use of composite materials can become difficult or expensive.
One prior art isolation technique has included use of shock mounts that support and isolate the disc drive from externally applied mechanical shocks, such as exemplified by U.S. Pat. No. 4,947,093 issued to Dunstan et al. and U.S. Pat. No. 5,469,311 issued to Nishida et al. Such an approach generally utilizes a number of externally disposed shock mounts, or shock absorbers, between the disc drive housing and the user environment. Because shock mounts are bulky and add to the effective size of the disc drive assembly, disc drive manufacturers have for the most part migrated away from the use of such devices.
Another prior art isolation technique involves the use of a chassis system, such as discussed in U.S. Pat. No. 5,140,478 issued to Yoshida and U.S. Pat. No. 5,777,821 issued Jul. 7, 1998 to Pottebaum. Such an approach involves the mounting of a chassis to exterior portions of the disc drive housing with an elastomeric damping material disposed therebetween. While reducing space requirements, the use of a chassis requires manufacturing and fitting of an additional component to the disc drive assembly, and can add weight and cost to the final product. Moreover, chassis systems also can have a significantly large force path which does not allow the dampening material to react quickly and effectively. In practice, shock mounts and chassis systems have been found operable, but not without attendant difficulties and limitations in vibratory isolation characteristics.
The feature of a low vibration disc drive assembly is especially desirable in disc drives subject to portable applications. Portability itself has its own requirements and objectives. In the computer world, specific designs for portability began in the early 1980's with personal computers weighing as much as around 14 kilograms, kg (30 pounds, lbs). These devices were supplied with substantial carrying handles and were more accurately described as "luggage" by users. This style of portable computer has since evolved into multiple generation "laptop" machines with substantially reduced weights and dimensions.
In parallel with these size-reduction trends in the computer world, the rigid disc drive industry has witnessed its own dramatic minimization over the last 40 years, from initial disc diameters of about 710 centimeters, cm (28 inches) in the 1960's to diameters today ranging from about 84 cm (3.3 inches) down to less than 25 cm (less than one inch).
These trends in disc drive form factors have been matched by complimentary improvements in data storage densities, performance, power requirements, and price. The increasing sophistication, availability, and universality of popular software during the last few years has also fueled the requirement for versatile, high-performance personal computers and has driven the hardware developments in the industry. Taking all of those trends together, the growing demand for laptop computers requires a matching availability of small, lightweight, high performance hard disc drives with the storage capability equivalent to that obtained on drives designed for desktop computers.
Accordingly, as disc drive track densities and performance requirements continue to increase and the disc drive assemblies get smaller, there remains a continual need for improved approaches in the art to isolate disc drives from externally generated rotational and translational vibrations and mechanical shocks. It is to such improvements that this invention is directed.